Differences in Phosphate and Parathyroid Hormone Concentrations over the Day among Patients on Hemodialysis

Background: Elevated serum phosphate and parathyroid hormone (PTH) concentrations are associated with cardiovascular events, bone disease, and mortality in patients on maintenance hemodialysis. Although circadian changes are known in people with CKD, it is unknown whether differences occur in these parameters over the course of a day in people receiving hemodialysis.

Methods: We used clinical data from Fresenius Medical Care US dialysis clinics to determine how the time of day when measurements were collected (hemodialysis treatment start time) may be associated with serum phosphate and PTH concentrations. We used harmonic regression to assess these associations while accounting for demographic data and treatment parameters.

Results: A total of 96,319 patients receiving maintenance hemodialysis were included in this analysis. Patients had a mean age of 64±14 years, 43% were women, and dialysis start times ranged from 3:00 am to 7:59 pm. The mean serum phosphate concentration was 5.2±1.5 mg/dl, and the median PTH was 351 pg/ml (interquartile range [IQR], 214-547). In fully adjusted models, serum phosphate had a nadir at 11:00 am of 4.97 (IQR, 4.94-5.01) mg/dl and a peak at 7:00 pm of 5.56 (IQR, 5.50-5.62) mg/dl. Serum PTH had a nadir at 9:00 am of 385 (IQR, 375-395) pg/ml and a peak at 7:00 pm of 530 (IQR, 516-547) pg/ml.

Conclusions: Among patients receiving maintenance hemodialysis, concentrations of PTH and phosphate before a dialysis session vary with the time of day that these values are measured. Consideration of whether these values were obtained at peak or nadir times of the day may be important in treatment decisions.